The present invention relates to a discharge lamp device, and more particularly to a discharge lamp device having an ultraviolet-ray shielding globe that surrounds the discharge lamp and is secured to the front surface of a base.
Recently, much interest has been shown in discharge lamps for automotive use because of their good luminous efficiency and color rendering properties as well as long life. However, a metal halide lamp, which is one example of a discharge lamp, generates a large quantity of ultraviolet rays together with visible light rays in the light emitted from the discharge gas (e.g., mercury gas, iodide gas, or Xe gas) contained in a discharge space. Ultraviolet rays having a wavelength in the range of 240-290 nm are believed to destroy protein molecules, ultraviolet rays having a wavelength in the range of 290-320 nm are believed to be a cause of skin cancer, ultraviolet rays having a wavelength in the range of 360-370 nm destroy a resin material that is located in the circumference of the discharge lamp device. There is thus a problem because of the potential harm to the human body, making it undesirable for a person to be subjected to this kind of illumination for a long time. The resin material in the circumference of the discharge lamp is also caused to prematurely deteriorate.
One conventional technique for reducing the harmful ultraviolet rays is disclosed in Japanese Patent Application Unexamined Publication No. Sho. 60-138845. This reference teaches a structure in which an ultraviolet-ray absorbing glass tube 4 is provided on the circumference of a discharge lamp 2, as shown in FIG. 6 herein. According to another conventional technique, as disclosed in Japanese Patent Application Examined Publication No. Sho. 62-53904, a discharge lamp 2 is tightly sealed within an ultraviolet-ray absorbing glass tube 6, as shown in FIG. 7.
In the first conventional technique, despite its simple structure in which the glass tube 4 is supported through leads 5, there is a problem in how to assuredly shield/absorb ultraviolet rays because the glass tube 4 has an opening portion 4a.
In the second conventional technique, there is a problem in that an inert gas such as N.sub.2 becomes trapped in the glass tube 6. Moreover, if the glass tube 6 is made a vacuum in order to reduce the adverse effects of temperature or pressure in the tightly sealed glass tube 6, the manufacturing equipment required and the actual manufacturing time become too expensive.
Japanese Patent Application No. Hei. 2-100503 discloses another discharge lamp. As shown in FIG. 14, a structure in which a discharge lamp 105 is supported by a pair of lead supports 103 and 104 projecting from an insulating base 102, and a cup-like ultraviolet-ray shielding globe 106 is fixed to a front surface of the base 102 by metal fittings 107. However, this approach has a problem in that the opening side of the globe is fixed to the base 102 by bending the metal fittings 107 or by fastening the outer circumference of the globe with band-like metal fittings. Therefore, because the globe cannot be easily fixed to the base, it can break if too much force is applied when fixing the globe to the base, and play (i.e., movement) may result in the fixing portion.
In consideration of the above problems, it has been proposed to integrally bond the globe to the base through an adhesive agent. In order to securely fix the globe to the base, the adhesive agent used is limited to an inorganic adhesive agent because of the high temperature associated with the discharge lamp and because the globe is made of a glass material. Assuming though that an inorganic adhesive agent is used, it is necessary to subject it to a heat treatment where the temperature reaches nearly 400.degree. C. However, the base, which is made of synthetic resin, cannot withstand such a high temperature.